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An improved EPMA analytical protocol for U-Th-Pbtotal dating in xenotime: Age constraints from polygenetic Mangalwar Complex,Northwestern India
Institution:1. UGC-Centre for Advanced Studies, Department of Geology, Presidency University, 86/1 College Street, Kolkata 700073, India;2. Atomic Minerals Directorate for Exploration and Research, Shillong, India;3. Atomic Minerals Directorate for Exploration and Research, Bengaluru, India;4. PPM Research Group, Department of Geology, University of Johannesburg, Auckland Park, Johannesburg, South Africa;1. Camborne School of Mines, University of Exeter, Penryn Campus, TR10 9FE, UK;2. Universidade de Brasília, Instituto de Geociências, Campus Darcy Ribeiro, 70910-900 Brasília, Brazil;1. Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611, USA;2. Department of Geology, University of Rajasthan, Jaipur 302004, Rajasthan, India
Abstract:EPMA U-Th-Pbtotal dating in U- and Th bearing minerals (e.g., monazite, zircon, and xenotime) is a low-cost and reliable technique used for retrieving age information from detrital, diagenetic and low to high-T metamorphic, as well as magmatic rocks. Although, the accuracy on measured ages obtained using EPMA is considered to be poor compared to isotopic ages, the superior spatial resolution, ability to integrate textural and age information by in-situ measurement, lack of sample damage and easier and cheaper data generation in EPMA make chemical dating a very valuable tool to decipher diverse petrological processes.This contribution presents an improved analytical protocol to obtain precise estimates of U, Th and Pb concentrations in xenotime. Results were tested on monazite standard (Moacyr pegmatite, Brazil; TIMS age: 487 ± 1 Ma) as the reference material. The proposed analytical protocol has been successfully applied to achieve an analytical uncertainty of less than 10% in U, Th and Pb measurements in xenotime. The protocol was further used to resolve polygenetic xenotime ages (ca. 1.82, 1.28 and 0.93 Ga) in metapelite samples from the Mangalwar Complex, Northwestern India. Monazites in the same samples were also analyzed and found to preserve the two younger ages (i.e., ca. 1.28 and 1.0 Ga). The obtained ages from the xenotime and monazite very well corroborate with the earlier published ages from the area validating the proposed analytical protocol.
Keywords:Xenotime  Monazite  Electron microprobe  Polygenetic ages
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